Enemies won't enter negotiations to end war

[Nicolas]

I started my first game a few days ago and I'm having a big problem. I've been at war with my three neighboring civs for maybe 50 turns now, and now matter what i do they keep ignoring my envoys and won't even discuss a peace treaty with me. I'm winning a pretty crushing victory, as they've yet to penetrate my borders and they have all lost cities to me, one even going from a 12 city empire to a single small island city, but no matter how soundly i trounce them they won't respond. I've had to devote almost all of my slider resources to luxuries to keep the riots down and i'm getting pretty tired of no science progress, and wiping them out isn't an option because two of them are enormous. Any ideas on how i can get them to stop sending my diplomats away?

[Lord Silvi]

Change your government to communism, monarchy or like that.
This lowers war weariness.
Forget science and go for military victory.

I too had your problem. But I didnt changed government.
I build up a powerful army, hit one of them very hard, and waited some years.
One day they will come to terms. And they will hack on each other.